Stricter legal requirements demand lower emission limit values for the exhaust gas of a motor vehicle for future vehicle models. It is already known that with internal combustion engines, which for example comprise four or more cylinders, the injected fuel quantity and thus the fuel-air ratio formed can differ between the individual cylinders. This is substantially due to the injection valves used, more preferably such as are controlled by a piezoelectric actuator, have differing manufacturing tolerances and are also subject to greater ageing influences.
It is furthermore known that with Otto-cycle engines a so-called lambda probe is used to determine the exhaust gas composition. The lambda probe is generally installed in the exhaust pipe near the engine and in front of the catalytic converter. The lambda probe is used to determine the residual oxygen proportion in the exhaust gas. Depending on the amount of the residual oxygen proportion more or less fuel is injected in the cylinders of the internal combustion engine or a corresponding control valve for returning the exhaust gas into the combustion chamber controlled. In this manner merely an average exhaust gas value can be set for the internal combustion engine, but not for an individual cylinder.
A further problem also consists in that the volume of an exhaust gas bank is relatively low because of the small distance between the individual cylinders as far as the catalytic converter and a smaller mixing distance for the exhaust gas is thus obtained than with an arrangement of the catalytic converter far away from the engine. Because of this, the influence of unevenness in the feeding of the fuel-air mixture to the individual cylinders is particularly pronounced.
Furthermore it is known that a fuel diagnosis (FSD, Fuel System
Diagnosis) is conducted on the basis of an adaptation value determined by a lambda controller. With this method for example the adaptation value of each exhaust gas bank is monitored. If the adaptation value exceeds a predefined limit over a certain period of time a fault is entered for the exhaust gas bank concerned. However, the fault message merely shows that a fuel or air fault is present in the exhaust gas bank concerned. The actual cause of the determined deviation cannot be located however. A defective fuel injector for example would trigger a fault entry but it would not be possible to clearly detect the injector itself as source of the fault.
In the USA it is additionally demanded by law for the next vehicle generations that will come on to the market that the uneven distribution in the fuel-air ratio is to be individually detected for each cylinder. However, a practical solution for the cylinder-selective uneven distribution in the fuel-air ratio that can be applied to coming vehicle generations has not become known as yet.